The present invention relates to a combination weighing machine, and is concerned in particular with the feeding of product from a bulk container into the individual weigh scales of the machine.
In U.S. Pat. No. 4,534,428 having the same inventors and assignee as the present invention, a control system is disclosed for regulating the amplitude and duration of vibratory feeders in a combination weighing machine. The feeders receive product from a bulk container or hopper at the top of the machine and distribute the product to the individual weigh scales as needed. The feeders are excited or vibrated with a controlled amplitude for a controlled period of time in order to feed a coarsely metered quantity of product into an accumulator that is associated with a specific weigh scale. Each of the weigh scales in the machine is fed in this manner. During each cycle of the machine the scales containing product are surveyed and the machine controller selects and dumps that combination of scales which produces a total amount of product that most closely approximates a targeted amount. The dumped scales are then refilled from their respective accumulators, and the accumulators are resupplied with product by their associated vibratory feeders.
The targeted amount of product may be specified as either a selected number of product pieces or a selected total weight of product. In the event that a targeted number of products pieces is sought, the weight signals from the individual scales are converted to whole numbers based upon a standard unit weight for one product piece of product, and then the combinations are formed based on the whole numbers. The technique, however, is error prone if the product pieces do not have a generally uniform weight.
With dry, fine divided, homogeneous and fluid-like products such as sugar or salt, peanuts, cereal flakes and small candies, the feeding of product to the individual weigh scales can generally be coarsely metered by controlling the amplitude and duration of the excitation of the vibratory feeders. However, for bulky, irregular, non-uniform or sticky products, such as chicken parts which can clump together, the feeding of product to the weigh scales is more difficult and sometimes imprecise. For example, if chicken legs are packaged with four legs per package, generally only one chicken leg should be loaded into each scale. However, since chicken legs frequently do not advance along vibratory feeders in a fluid-like state, a scale may end up with none or sometimes three or more chicken legs. As a consequence reliance upon vibrator amplitude and duration control is not satisfactory.
It is accordingly a general object of the present invention to provide a more accurate method and apparatus for feeding products, particularly products that come in the form of sticky, irregular or non-uniform pieces.